cmi 4.5 exhaust
 

i have cmi 4.5 in exhaust system with the riser that bolts onto the header(i believe its called split top or something like that),and the steel tip runs straight through the transom (no rubber etc.), how much power are these good for? cmi claims 750, but we were interested in bringing our 600s up to 850, and wanted to know how detrimental they would be to the performance. thanks